1. Field of Invention
The present invention relates to a pixel circuit, and more particularly relates to an AMOLED compensation pixel circuit.
2. Description of Related Art
FIG. 1 shows an organic light emitting diode pixel circuit of the prior art. The pixel circuit is a voltage type pixel circuit. The pixel circuit has a light emitting diode 110, a driving transistor 130, a capacitor 150, a first switch 125, a second switch 145, a third switch 160, and a forth switch 170. A drain 136 of the driving transistor 130 is coupled to a second end 118 of the light emitting diode 110 through the first switch 125. The second switch 145 is coupled between a source 132 of the driving transistor 130 and a power source terminal 140. The capacitor 150 is coupled between a gate 134 of the driving transistor 130 and the ground terminal 120. The third switch 160, controlled by a first scan signal (SCAN1), is coupled between the source 132 and the gate 134 of the driving transistor 130. The fourth switch 170, also controlled by the first scan signal (SCAN1), is coupled between the second end 118 of the light emitting diode 110 and a data line 180.
The first switch 125 and the second switch 145 are controlled by the second scan signal (SCAN2). The second switch 145 is to couple or decouple the source 132 of the driving transistor 130 and the power source terminal 140. The first switch 125, the second switch 145, the third switch 160, and the fourth switch 170 are transistors.
The pixel circuit operates in a reset period, a programming period, and a display period sequentially. During the reset period, all of the four switches are turned on; during the programming period, the first switch 125 is turned off, the second switch 145 is turned off, the third switch 160 is turned on, and the forth switch 170 is turned on; during the display period, the first switch 125 is turned on, the second switch 145 is turned on, the third switch 160 is turned off, and the forth switch 170 is turned off. The first scan signal (SCAN1) is asserted to turn on the third switch 160 and the forth switch 170 during the reset period and the programming period, and de-asserted to turn off the third switch 160 and the forth switch 170 during the display period. Hence, the data signals (VDATA) from the data line 180 are transmitted to the pixel circuit during the programming period
The drawback of the conventional pixel circuit is as follows. The pixel circuit has small aperture ratio since it has five transistors and one capacitor. Also, during the reset period, there is current flowing from the power source terminal 140 to the data line 180, then to the ground terminal 120. Besides, the pixel circuit has large power consumption since the power path involves three transistors, including the second switch 145, the driving transistor 130, and the first switch 125.